Theoretical studies on the ground and excited states for a series of terpyridyl platinum ( II) complexes

To explore the substituents how to affect the excited state for the the terpyridyl Pt(H) complexes, we calculated a series of complexes [Pt(trpy) C C ≡ CC₆H₄R]⁺ [trpy = 2,2' ,6,2'-Terpyridine; R = NO₂ (1), Cl(2), H(3) and CH₃(4)]. MP2 and CIS methods were used to optimize the ground and excited states for the four complexes, and TDDFT method at B3LYP level was employed to obtain their phosphorescent emission spectra. The results reveal that the lowest-energy phosphorescence of compound 1 can be assigned as the Pt-C ≡ C→trpy charge transfer (³MLCT/ ³LLCT) transitions and perturbed by the π→π transition localized on the C₆H₄NO₂ moiety, due to the stronger electron-withdrawing ability of NO₂ and the possible resonance structures in C ≡ CC₆H₄NO₂. But the other three complexes were only attributed to ³MLCT/³LLCT characters. In addition, the excited-state structures are similar to those of the ground-state ones, which is in agreement with the small Stokes-shift in the experiments.